Bath for plating bright gold



United States Patent BATH FOR PLATING BRIGHT GOLD Barnet D. Ostrow, North Bellmore, and Fred I. Nobel, North Valley Stream, N. Y.

N0 Drawing. Application November 19, 1954, Serial No. 470,136

7 Claims. (Cl. 204-46 The present invention is directed to electroplating baths, more particularly to a gold cyanide plating bath adapted to produce bright deposits which no not require brushing or bufling.

Gold plating baths capable of producing bright depOSitshaVe been known and used. The degree of brightness obtained by such baths has been about equivalent to the brightness obtained by the use of present day bright nickel baths. However, such bright gold baths required certain special equipment of a highly specialized character in order to obtain-(the optimum results in the operation. Such equipment required close attention and a high degree of skill on the part of the operator. Therefore there has been a need for a bath which was adapted to give bright gold deposits without the necessity of special equipment or special attention on the part of the operat-or.

The present invention is intended and adapted to overcome the disadvantages inherent in prior bright gold baths, it being among the objects of the present invention M a bath which is capable of reproducing in the gold depo it the brightness present in the basis metal.

It is also among'the objects of the present invention to provide a bathgiving a bright gold deposit which requires no scratch brushing or coloring.

It is further among the objects of the present invention to provide a bath of the character described, which is simple in operation, which is easy to control and which is capable of providing optimum operating results.

In practicing the present invention there is provided a cyanide bath of well-known character consisting essentially of gold cyanide and free alkali metal cyanide in solution with water. In accordance with the invention, there is added to the bath two types of substances, one of which is a condensation product of certain carboxylic acids and certain amino acids. There is also present in the bath in relatively small amount a soluble nickel salt and/or a soluble tin salt. The invention also contemplates the presence at the same time of both nickel and tin salts.

The condensation product is made by reacting a fatty acid having from 8 to 18 carbon atoms with an amino acid. The resulting condensation product is believed to have the following structural formula:

wherein M represents hydrogen and alkali metal, R represents an alkyl radical having 7 to 17 carbon atoms, R represents a lower fatty acid, an alkyl monoalcohol, ester thereof, ether thereof, the alkyl radicals of which have 1 to 3 carbon atoms and hydrogen, and R represents methylene, ethylene and propylene, together with a water soluble salt of a metal taken from the class consisting of nickel and/or tin. The amount of said condensation product ranges from 1 to 100 grams per liter and good results are obtained by the use of 2530 grams per liter in the bath.

The nickel may be present in the form of any soluble salt thereof which does not interfere with the plating operation, such as the sulphate, cyanide and the like, the amount of nickel present in the bath ranging from 0.10 to 50 grams per liter. Any such salt will upon addition to the bath form complex alkali metal cyanide. The tin is also present as a solublecompound and it has been found that an excellent form is that of alkali metal stannates, the amount of tin present in the bath ranging from 0.01 to 20 grams per liter. Mixtures of salts of this character may be added to the bath.

The following are specific examples showing a number of baths which are suitable for the present purposes. The formulas of the following examples show the relative amounts of the constituents in grams per liter. Electroplating takes place at temperatures between 70 and F. with vigorous agitation for the best results. The current densities range from 0 to 20 amperes per square foot, depending on the gold concentration.

Example 1 Gold as KAu cyanide 7.5 Nickel as KzNi cyanide 3.0 Potassium stannate 4.0 Free potassium cyanide 80.0 N-methylglycine-lauric acid potassium salt 20.0

Example 2 Gold as KAu cyanide 10.0 Potassium stannate 6.0 Free potassium cyanide 90.0 N-ethanolglycine-myristic acid sodium salt 30.0

Example 3 Gold as KAu cyanide 4.5 Nickel as Ni sulphate 20.0 Free potassium cyanide 15.0 N-acetylglycinemyristic acid-sodium salt 25.0

Example 4 Gold as KAu cyanide 5.5 Nickel as KzNi cyanide 3.5 Free potassium cyanide 20.0 N-ethyletherglycine-oleic acid sodium salt 35.0

Example 5 Gold as NaAu cyanide 9.0 Sodium stannate 5.5 Free sodium cyanide 25.0

N-methylrnethylateglycine-stearic acid sodium salt 20.0

Methods of making the condensation products of the fatty acids and amino acids are well-known.

Such compounds made from sarcosine have been mentioned in the prior art for use in silver cyanide plating baths. However, gold deposits obtained from gold cyanide plating baths containing such condensation products, are not bright when the bath contains only these complex condensation products as brighteners. It is only when there is present in the bath in addition thereto of a soluble compound of tin or nickel, or a mixture of such compounds of the two metals, that bright gold deposits can be obtained. And the optimum brightness of such deposits are obtained when both tin and nickel are present together with the organic condensation product.

Such a combination has an important advantage in connection with the operation of the bath. The presence of the condensation product increases substantially the tolerance of the plating bath for organic impurities and contamination. While in the prior art it had been suggested to use other precious metals for the purpose of producing bright gold deposits, such additions increase costs to a substantial extent and Fnrflnm-mnw. a... 1U 1U.

wherein M represents a radical taken from the class consisting of hydrogen and alkali metal, R represents an alkyl radical having-7 to 17 carbon atom's,'l1 represents a radical taken from the class'consisting of a lower fatty acid, an alkyl monoalcohol, ester thereof, ether thereof,

the alkyl radicals of which have 1 to 3 carbon atoms and hydrogen, and R" represents a radical taken from the class consisting of methylene, ethylene and propylene, the amount of said reaction product being from-1 to 100 ms./ liter, together with the water soluble salts of nickel and tin in sufficient amount to exert a brightening eifcct on the plated gold.

2. In a bright gold plating bath conslstingessentially" of gold cyanide and free alkali metal cyanide in water,

solution, the improvernerltwhich comprises the addition of said bath-of a condensation product of a fatty acid having 8 to .18 carbon atoms with an amino acid and having the following structural formula:

R-fil-N-R b it"COOM.

wherein M represents a radical taken from the class consistingof hydrogen and alkali metal, R represents an alkyl radical having 7 to 17 carbon atoms, R represents a radical taken from the class consisting of a lower fatty acid, an alkyl monoalcohol, ester thereof, ether thereof, the alkyl radicals of which have 1 to 3 carbon atoms and hydrogen, and R" represents a radical taken frorn'the class consisting of methylene, ethylene and propylene, the

amount of said reaction product being about 25-30 g ns/liter, together with the water-soluble salts of nickel and tin in sufficient amount to exerta brightening effect on the plated gold.

3. In a bright gold plating bath consisting essentially of gold cyanide and free alkali metal cyanidein water gnls./liter and the amount of tin being from 0.01 to 20 gins/liter: f

4. In a bright gold plating bath consisting essentially of gold cyanide and free alkali metal cyanide in water solution, the improvement which comprises the addition to said bath of the following composition in grams per liter:

Tin as alkali metalstannate 0.0120

Nickel as soluble nickel salt 0.l050 Condensation product of fatty and amino acid 1-100 said tin and nickel'being present, in suflicient amount to exert a brightening effect, said condensation product having the following structural formula:

wherein M represents a radical taken from the class consisting of hydrogenand alkali metal, R represents an alkyl radical having 7 to 17 carbon atoms, R represents a radical taken from the class consisting of a lower fatty acid, an alkyl mono-alcohol, ester thereof, ether thI60ll the alkyl radicals of which have 1 to 3 carbon atoms and hydrogen, and R" represents a radical taken from the class consisting of methylene, ethylene and propylene.

5. In a bright gold plating bath consisting essentially of gold cyanide and free alkali metal cyanide in water q solution, the improvement, which comprises the addition to said bath of the'following composition in grams perliter: Y

Tin as alkali metal stannate 0.01-20 Nickel as soluble nickel salt 0.10- Condensation product of fatty and amino acid 1-100 said tin and nickel being present -in sufficientamount to. exert a brightening efiect,said condensation product being of N-methyl. glycine With. an acid taken fronl the/- class consisting of" oleic, stearic, palmitic, laf ricaand myristic; i 1:

6. In a bright gold plating bath consistingies'sentially of gold cyanide and free alkali metal cyanide inwater' solution, the improvement which comprises the addition solution, the improvement which comprises the addition to said bath of a condensation product of a fatty acid having '8 to 18 carbon atoms with an amino acid and havingthe following structural formula:

wherein M'represents a radical taken from the class consisting of hydrogen and alkali metal, R represents an alkyl radical'having 7 to 17 carbon atoms, R represents a radical taken from the class consisting of a lower fatty acid, an alkyl monoalcohol, ester thereof, ether thereof, the alkyl radicals of which have 1 to 3 carbon atoms and hydrogen, and R represents a radical 'taken from the class consisting of methylene, ethylene and propylene, the amount of said reaction product being about 1400 grams per liter, together with the Water-soluble salts of nickel and till, the amount of nickel being from 0.1 to 50 to said bath of the following composition in gr'amspcr' said tin and nickel being present in sufficient amount to exert a brightening effect, said condensation product being of N-methyl glycine with the mixed acids of coconut type oil.

7. A bath according to claim 1 in which the amino acid is a glycine.

References'Cited inthe file of this patent FOREIGN PATENTS France Feb. 18, 1953 OTHER REFERENCES Serial No. 351,241, Weiner (A. P. C), published May 18, 1943.

liter: 7 j Tin as alkali metal stannate @0101-20." Nickel as soluble nickel salt 0 ,l0-50"* Condensation product of fatty and amino acid 1-1 00 

1. IN A BRIGHT GOLD PLATING BATH CONSISTING ESSENTIALLY OF GOLD CYANIDE AND FREE ALKALI METAL CYANIDE IN WATER SOLUTION, THE IMPROVEMENT WHICH COMPRISES THE ADDITION TO SAID BATH OF A CONDENSATION PRODUCT OF A FATTY ACID HAVING 8 TO 18 CARBON ATOMS WITH AN AMINO ACID AND HAVING THE FOLLOWING STRUCTURAL FORMULA: 